Crowds will start pouring into NRG Park on Tuesday for opening day of the rodeo, likely braving rain and chilly weather. Across the damp and silent carnival ground in NRG Arena, merchants already were selling leather work, cowboys were competing and volunteers were talking about how to keep the hay dry. Horses and their riders will compete through Thursday in the second stop of the World Series of Cutting and related events, where riders already have ranged from a six-year-old girl whose legs don't reach past the horse blanket to professionals who win millions of dollars each year. The rider guides the horse with reins and thighs to a targeted calf but drops their hands once the young cow is alone, letting the horse lead as it blocks the cow's attempts to dart back into the herd, said Jennifer Harmel of Conroe, chairwoman of the Cutting Horse Committee.